Sheet steel and sections, tubes and composite constructions manufactured therefrom



p 20, 1965 A. wo RBAUER 3,273,976

S TIONS T HEET STEEL AND SEC B S AND COMP TE GONSTRUCTIONS MANUFACTUREDTHEREFRO Filed March 16, 1964 6 Sheets-$heet 1 VENT ALFRED w RBAU M.fimMTM HIS ATTORNEYS Sept. 20. 1966 A. WOGERBAUER 3,273,976

SHEET STEEL AND SECTIONS, TUBES AND COMPOSITE CONSTRUCTIONS MANURRRRRRRRRRRRRRR 0M Filed March 16, 1964 6 Sheets-Sheet 2 /1 7 H64 l%F-\%\\\ xx ,4 4 f ne? f 4 Fi F/G.8

ALFRED WOGER u BY W- MMMM H IS ATTORNEYS Sept. 20, 1966 A, WOGERBAUER3,273,976

SHEET STEEL AND SECTIONS, TUBES AND COMPOSITE CONSTRUCTIONS MANUFACTUREDTHEREFROM 6 Sheets-Sheet 5 Filed March 16, 1964 H INVENTOR ALFREDWOGERBAUER H IS ATTORNEYS Sept. 20, 1966 A. WOGERBAUER 3,273,976 TUBESAND COMPOSITE CONSTRUCTIONS SHEET STEEL AND SECTIONS,

MANUFACTURED THEREFROM 6 Sheets-Sheet 4 Filed March 16, 1964 FIG. /5

FIG/E FIG/7 INVENTOR ALFRED WOGERBAUIER H IS AT TO RN EYS p 1965 A.WOGERBAUER 3,273,976

SHEET STEEL AND SECTIONS, TUBES AND COMPOSITE CONSTRUCTIONS MANUFACTUREDTHEREFROM 6 Sheets-Sheet 5 Filed March 16, 1964 INVENTOR S a m m N B R RO E w m A W .6 V.- H we R Sept. 20, 1966 A. WOG ERBAU ER SHEET STEEL ANDSECTIONS TUBES AND COMPOSITE CONSTRUCTIONS Filed March 16, 1964 FIG. 2/

AV AV AV MANUFACTURED THEREFROM 6 Sheets-Sheet 6 INVENTOR ALFREDWOGERBAUER HIS ATTORNEYS United States Patent 3,273,976 SHEET STEEL ANDSECTIUNS, TUBES AND COM= PQSITE CUNSTRUCTIONS MANUFACTURED THEREFROMAlfred Wagerbauer, Linz, Austria, assignor to Vereinigte OsterreichischeEisenund Stahiwerlre Ahtiengeseilschaft, Linz, Austria, a company ofAustria Filed Mar. 16, 1964, Ser. No. 351,932 Claims priority,application Austria, Mar. 19, 1963, A 2,166/63 6 Claims. (Cl. 29-180)This invention relates to steel sheets and sections, tubes and compositeconstructions manufactured therefrom, having a yield point of more than50 kg./sq.mm., a tensile strength of more than 55 kg./sq.mrn., and anelongation of at least 8%.

For steel sheet and structural members having the mentioned parametersonly steels of special grades, such as St 60 or St 70, which areclassified as low all-oy steels, and heat treatable steels, which have ahigher content of alloy elements, such as manganese and vanadium, havehitherto been used. Steels having the mentioned characteristics, i.e.the low alloy structural steels and the higher alloy heat treatablesteels, had to have a carbon content of considerably more than 0.30%, inorder to achieve the required strength values. Steels having such highcarbon content, however, can no longer be welded, or they require aspecial melting treatment, which materially increases the manufacturingcosts and, consequently, the price of these steels.

It has been known that by cold working steel sheet or strips thestrength values of these materials can be increased. As cold workingmeasures it has been proposed to stretch, roll or draw the strip. Duringcold rolling the thickness or gauge of the sheets is reduced in severalpasses, this requiring voluminous and expensive installations. Also thehardening by cold stretching is a time consuming and uneconomicalprocess which causes an undesirable loss of material due to therequirement of gripping the sheets. Drawing the sheets on drawingbenches has not proved satisfactory either. This process was limited tocomparatively narrow strips, a lot of waste material resulting for thesame reasons as in stretching; furthermore lubrication is an unsolvedproblem in drawing processes.

It is further known to provide steel sheets with ornamental patterns bycoining or stamping. A stamped sheet is, for instance, the so-calledhammered sheet. By this process an increase of the strength values isobtained as a secondary efiect. Primarily, however, the object of theknown process is to obtain decorative effects.

As a further measure of strain-hardening sheet steel by cold working ithas been proposed to impart to a hot rolled strip a ridge-and-grooveprofile by drawing or rolling, then flattening the ridge-and-grooveprofile and finally shaping the steel sheet treated in this way intosections. Flattening the ridge-and-gro-ove profile causes, however, achange of width of the strips, depending on the groove depth chosen forprofiling.

Finally, strain hardened steel sheet having lasting ridgeand-grooveprofiles or a buckled surface are known, which have been used forspecial construction purposes.

Up to now, it has not been possible, however, to achieve and guaranteeto the buyers reproduceable results. Due to the cold working thematerial frequently became so brittle that it could no longer beprocessed, as the yield point was highly increased, whereas theelongation at break was reduced to nil. Such a material is no longeruseful for the manufacture of sections, tubes and compositeconstructions.

3,273,976 Patented Sept. 20, 1966 It is an object of this invention toavoid the disadvantages and difficulties described. The invention isbased on the recognition that the degree of deformation of a coldworking treatment used for strain hardening has to range betweenspecific limits, in order to ensure a reproduceability of the results,particularly of the pair of values: yield pointelongation, which is ofpractical importance.

Accordingly, the invention provides a sheet steel and sections, tubesand composite constructions manufactured therefrom, respectively, havinga yield point of more than k g./sq.mm., a tensile strength of more thankg./sq.mm., and an elongation of at least 8% which are characterized inthat the work pieces consist of steel having a carbon content of lessthan 0.30%, and are provided with a ridge-and-groove profile in whichthe inner radius of curvature of the grooves is smaller than three timesthe sheet or wall thickness and the ratio of depth to pitch of theridge-and-gr'oove profile amounts to 1:15 to In particular, it isproposed for the composition of the material that the carbon content is0.15 to 0.19%, the silicon content 0.06 to 0.15%, the manganese content0.30 to 0.45 the phosphorus content less than 0.09%, preferably not morethan 0.03%, and the sulphur content less than 0.06%, preferably not morethan 0.04%.

The strength values obtained by the cold working are in a certainrelation also with the sheet thickness. Under the mentioned conditionsthe sheet thickness should be 1 to 6 mm., preferably 1.5 to 4 mm.

In order to ensure the weldability of such work pieces, it is providedaccording to a further proposal of the invention that a steel stripprovided according to the invention with a ridge-andgroove profileremains non profiled in narrow marginal zones, these zones serving forthe welding in the subsequent manufacture of tubes, compositeconstructions, etc.

The eifect of the ridge-and-groove profiling according to the inventionis essentially due to the fact that the profiled work piece isalternately bent and stretched perpendicularly to the direction of theridges and grooves, the bent zones corresponding in the proportion ofhalf the pitch to the grooves and the stretched zones being interposed.

The invention is explained in more detail in the drawings. FIGS. 1, 2and 3 are sectional views of ridge-andgroove profiled strips as viewedperpendicularly to the direction of the grooves. FIGS. 4 to 8diagrammatically illustrate in like representation the manufacture ofsuch strips. In FIGS. 9, 10 and 11 perspective views of sheets havingdifferent groove directions are shown.'

FIGS. 12 to 17 show, partly in sectional view and partly in top view,composite constructions made of strips provided according to theinvention with a ridge-and-groove profile. FIGS. 18 to 20 representother composite constructions in perspective view, and FIGS. 21 and 22illustrate a process and an apparatus for manufacturing compound sheets.

In FIGS. 1 to 3, letter a denotes the sheet thickness, r the innerradius of curvature of the grooves, t the depth of the grooves and a thepitch of the ridge-and-gr-oove profile, varying ratios of r:d and tzabeing represented in r the three figures.

In FIGS. 4 to 8 the individual steps of the manufacture of suchridge-and-groove profiled sheets and the formation of edged andstretched zones in the profile-d sheet are illustrated. The originallyunworked sheet 1 is passed into the roll gap between upper roll 2 andlower roll 3 and initially engaged by the rolls in such manner that theridgeand-groove profile provided on the working surface of the rollscontacts the sheet with its ridges. In this position the roll gap isdesignated by A '(FIG. 4). When the roll gap is reduced (roll gap A inFIG. and roll gap A in FIG. 6), the sheet 1 is continuously bent aroundthe crests of the ridges, any peripheral recession trom the edges of thestrip being eliminated. The layer 4 originally disposed in the center ofthe sheet increases in length between two adjacent bends, so that thesheet is edged on the inside of the bending zones and is stretched onthe outsides of the bending zones as well as in the interposed non-bentzones in the proportion of half the pitch. In this way the sheet isstrain-hardened across its entire cross-section. Upon decreasing theroll gap the yield point and the tensile strength are in creased, whilethe elongation decreases. The difference between the original roll gap Aand a reduced roll gap A or A amounts to the groove depth applied to thesheet (indentation), which in FIGS. 1 and 2 is designated by t. Thegroove depth t plus the initial sheet thickness amounts to the nominalthickness s of the strain hardened sheet (FIG. 6). If the roll gap isreduced by further screwing down of the upper roll to such an extentthat it is completely filled with the strain hardened sheet (A; in FIG.7), the alternating bending and transverse stretching is finished. Upona further reduction of the roll gap, e.'g., to A in FIG. 7, a breakdownrolling is superimposed to the finished phase of strain hardening. Thisresults in a further increase of the strength values and enables asizing of the sheet thickness, whereby it is possible to avoiddeviations from the desired thickness which usually occur in hot rolledsheets and to achieve the same accuracy of the thickness dimensions asin cold rolled strips.

In FIG. 8 an extreme case is illustrated, wherein a sheet is strainhardened solely by alternating bending. The bent zones immediatelyadjoin to each other, without having zones of pure stretch drawinginterposed therebetween, which may be accomplished by a suitable choiceof the variable process conditions (adjustment of the roll gap relativeto the sheet thickness).

In the following examples, the yield point, tensile stress andelongation values obtained in steel sheets of grades St 37, St 42 and St44 are given. In several tests the dimensions of inner radius r ofcurvature, sheet thickness d, groove depth t and pitch a were varied;the exact chemical composition of the material is likewise given.

Example 1.Strip No. 948,569, chemical composition: 0.01% C, 0.11% Si,0.29% Mn, 0.009% P, 0.020% S (St 42).

h Initial value (non-hardened sheet).

Example 2.Strip No. 948,567, chemical composition: 0.12% C, 0.09% Si,0.35% Mn, 0.011% P, 0.025% S (St 42).

Test a r t ds or, a, 6 No.

mm. mm. kq./sq. mm. kqJsq. mm. percent 0. 00 l. 84 33. 6 44. 5 30. 5 0.50 2. 34 55. 5 57. 2 8. 2 0. 56 2. 40 55. 0 57. 3 8. 2 0. 61 2. 45 56. 057. 6 7. 9

8 Initial value (non-hardened sheet).

1 Example 3.Strip No. 948,572, chemical composition: 0.09% C, 0.13% Si,0.45% Mn, 0.012% P, 0.026% S, 0.004% N (St 42).

Test a r t ds a. a, 6

mm. mm. mm. mm. kq./sq. mm. lcq./sq. mm. percent 1a-... 5 1. 25 0.00 1.78 32. 4 43. 4 30. 7 2 5 1. 25 0.42 2. 20 54. 4 55.1 8.6 3 5 1. 25 0.522. 30 54. 0 55. 0 8.0

Initial value (non-hardened sheet).

Example 4.Strip No. 948,568, chemical composition as in Example 2.

Si, 0.32% Mn, 0.09% P and 0.025% S (St 42).

a T i d a, a, 6

a-l q-l mm mm. mm. mm. sq. mm. sq. mm. percent Starting material. 1. 531. 9 43. 7 33. 0 Strain hardened 4 1. 6 0. 6 l. 5 57. 6 58. 6 8. 5

Example 6.Che-rnical composition as in Example 5 a r t d (T. a, 6

kg./ kg./ mm. mm. mm mm; sq. mm. sq. mm. percent Starting material. l. 532. 8 44. 6 26.0 Strain hardened 4 1. 6 0. 4 1. 5 53. 9 57. 4 9. 9

Example 7 .Chemical composition as in Example 5.

a T i ll 7 0; 5

kg./ kq./ mm mm. mm. mm. sq. mm. sq. mm. percent Starting material- 1. 538. 5 48. 4 29. 0 Strain hardened 10 2. 5 1. 4 l. 5 55. 4 62. 5 12. 3

Example 8.-Chemica1 composition as in Example 5.

a r t d 0'; a, 5

M kq-l mm. mm. mm. mm. sq. mm. sq. mm. percent Starting material. 1. 537. 8 46. 5 28. 5 Strain hardened 10 3. l5 2. 4 1. 5 63. 5 64. 7 8. 0

Example 9. Chemical composition: 0.10% C, 0.11% Si, 0.29% Mn, 0.009 Pand 0.020% S (St 42) Test No. a r t d a, a, 5

kg./ kg./ mm. mm. mm. mm. sq. mm. sq. mm. percent The results of furthertests using sheet steel of grade St 44 are evident from the followingtable:

Chemical composition: 0.17% C, 0.25% Si, 0.68% Mn, 0.025% P, 0.028% S,0.0055% N (St 44).

a r t d a, a, 8

kg./ kg./ mm. mm mm mm sq. mm. sg.mm. percent Starting material 1.8735.5 51.8 28.5 Strain hardened 4 1 0.12 1.99 50.7 55.0 20.7 Startingmaten 1.85 38.0 52.4 26.3 Strain hardened 4 1 0.16 2.01 51.6 55.8 19.4 4l 0. 16 2. 01 52. 2 55. 6 21. 2 4 1 0.16 2.01 51.3 55.2 19.4 4 1 0.162.01 51.1 55.1 20.5 Starting material. 1.85 37.6 52.6 25.4 Strainhardened 1 4 1 0.2 2. 05 55.0 56.8 15.1 4 1 0.2 2.05 55.3 57.0 14.5 4 10.2 2.05 55.9 57.4 12.0 4 1 0.2 2.05 54.6 56.8 16.5 Starting material 1.85 37.0 51.8 27.6 Strain hardened 4 1 0.24 2.09 58.4 60.2 9.5 4 1 0.242.09 58.4 60.4 9.9 4 1 0.24 2. 09 57.0 58.7 12.4 4 1 0.24 2.09 58.6 60.110.1 Starting material- 1.83 36.6 51.4 29.1 Strain hardencd 4 0.2 2.0353.0 55.5 18.4 4 2 0.2 2.03 53.6 55.8 19.5 Starting materi 1.85 36.251.9 29.9

Strain hard- 4 2 0.3 2.15 56.8 58.8 15.0 ened l 4 2 0.3 2.15 55.7 58.615.0 Starting inatcrial 1.85 36.8 51.6 30.1 Strain hard- 4 2 4 2.25 58.760.6 12.1

ened

4 2 0.4 2. 25 59.4 61.0 8.90 Starting ma teri 1.85 35.6 51.4 28.5 Strainha ened 1.6 0 3 2.15 54.2 56.3 15.5 5 1.6 0 3 2.15 54.3 56.3 17.9Starting material 1.85 37.2 52.0 27.6 Strain hardened 5 1.6 0.4 2. 2557.4 59.3 8.8 5 1.6 0.4 2.25 57.9 59.2 11.7

In FIG. 9 a strip sheet is illustrated which comprises three zoneshaving ridge-and-groove profiles running in crosswise directions. Thelateral zones 6 and 7 are longitudinally grooved, and the interposedmiddle zone 8 is transversely grooved. The maginal zones 5 arenonprotfiled and nonhardened so that they are easily weldable. Sheets ofthis type are particularly suitable for the manufacture of heatexchangers.

In FIG. a strip sheet is shown, which comprises two nonprofiled(nonhardened) marginal zones 9 and 10 and an interposed middle zone 11.The middle zone 11 has crossing diagonal grooves 12, 12'. A similardesign is shown in FIG. 11. There, the middle zone 11 is again providedbetween two nonhardened marginal zones 9 and 10 of a sheet strip and hassuperimposed ridge-and-groove profiles 13, 13'.

FIGS. 12 to 14 illustrate in two sectional views and in a plan view acompound sheet consisting of a longitudinally grooved upper sheet 15 anda transversely grooved lower sheet 16. These sheets are connected toeach other at the points of intersection 17 of the longitudinal ridgeswith the transverse ridges by welding, pref erably resistance welding.

In FIGS. 15 and 16 again a compound sheet is shown which consists ofthree single sheets strain hardened by a ridge-and-groove profile.Between a longitudinally grooved upper sheet 18 and a likewiselongitudinally grooved lower sheet 19 a transversely groovedintermediate sheet 20 is arranged. The three sheets are connected witheach other at the points of intersection of the ridges by welding.

FIG. 17 shows a composite body of the hollow panel type. It consists ofa longitudinally grooved upper sheet 21, a likewise longitudinallygrooved lower sheet 22 and a zigzag-shaped middle part 23 serving as aspacer and forming a strutting. The middle part 23 may also be made of atransversely grooved sheet so that at the junctures of the middle partwith the sheets 21 and 22 longitudinal and transverse ridges againintersect and can be connected in a simple manner by resistance Welding.

FIGS. 18, 19 and 20 illustrate other structural panels formed ofsandwich boards of the type shown in FIGS. 12 and 13. In FIG. 18 atrapezoidally bent middle part 26 is arranged between an upper compoundsheet 24 and a lower compound sheet 25, the middle part consisting of asingle, longitudinally grooved sheet. Similarly, in FIG. 19 a middlepart 29 of transversely grooved sheet is welded in between the twocompound sheets 27 and 28. FIG. 20 shows a structural panel, in whichnot only the outer sheets 30 and 31, but also the middle part 32 consistof a compound sheet of the type illustrated in FIGS. 12 and 13.

In FIG. 21 an apparatus for the continuous manufacture of compoundsheets, eg of the type shown in FIGS. 12 and 13, is illustrated. Theapparatus comprises reels for unwinding coiled hot rolled strips,devices for applying a ridge-and-groove profile viz. selectively alongitundinal or a transverse ridge-and-groove profile, a weldingequipment for connecting the ridge-and-groove profiled single sheets,and a device for winding up or for shearing to length the compositeconstructions. The strip 54 is reeled off coil 55, and simultaneouslystrip 56 is reeled 011 coil 57. The strip 54 comes via the reversingroller 58 to the transverse-grooving rolls 59 and 60, in the roll gap ofwhich it is imparted a transverse ridge-andgroove profile andstrain-h-ardened. Upon strain-hardening, the strip 54 is taken off viathe reversing rollers 61 and 62. Simultaneously the strip 56 is fed viathe reversing roller 63 into the roll gap of a two high stand comprisingrolls 64 and 65. The longitudinal-grooving rolls 64 and 65 impart to thestrip a ridge-and-groove profile in the longitudinal direction. Arrangedbehind the twohigh there may be a four-high stand comprising thebacking-up rolls 66 and 67 and the breaking-down rolls 68 and 69. Thelongitudinally grooved sheet 70 now is passed straight on to the weldingequipment, where it meets with the first strip, here designated bynumeral 71, which is fed via the reversing roller 72. The speed of thetwo strips must be synchronized, which may be accomplished by means ofknown type. Such a synchronizing means is indicated in FIG. 21 by theroll 72 being displaceable from the position drawn in fully inked linesto the position drawn in dash lines. The shortening and lengthening,respectively, of the loop formed by the transversely grooved strip 71which is due to the movability of roll 72, may be utilized -forsynchronizing.

The welding equipment comprises the current supply roller 73 and thecurrent supply roller 74. To these two electrode rollers welding currentis supplied from the transformer 75 via the sliding contacts 76 and 77.The electrode rollers extend over the entire width of the strips 70 and71, which are continuously passed through between the electrode rollersin superposed position. Owing to the power concentration at the pointsof intersection of the longitudinal ridges with the transverse ridges ofthe two superposed sheets 70 and 71, transverse rows of intersectionsare successively welded together. For welding, alternating current or,preferably, direct current may be used. The welded compound sheet 78 maybe out behind the welding machine into sheets of desired length by meansof "blades 79 and 80.

In FIG. 22 the gap between the electrode rollers is illustrated on anenlarged scale. Numerals 81 and 82 denote the course of the weldingcurrent, which is concentrated at the crossing point 83 and there weldstogether sheets 70 and 71.

Composite constructions according to the present invention may be usedwith advantage in building practice for walls, ceilings, doors, gates,as clothing or the like. A preferred field of application further liesin car building. In addition to the advantages of the invention alreadymentioned which are manifested by an increase of the strength propertiesand a simultaneous maintainance of an elongation sufiicient for shapingoperations, it is to be remarked that the building safety of buildingsmade with structural elements according to the present invention isincreased and a favorable architectural effect is achieved. More-over,the costs, as compared with those of known structural elements which hadto be made of considerably more expensive materials, are materiallylower.

What I claim is:

1. Strain hardened sheet steel having a yield point of more than 50kg./mrn., a tensile strength of more than 55 kg./sq. mm., and anelongation of at least 8%, the sheet steel being made of steel having acarbon content of less than 0.30% and being provided with aridge-andgroove profile in which the inner radius of curvature of thegrooves is smaller than three times the sheet thickness and the ratio ofdepth to pitch of the ridge-and-groove profile amounts to 1:15 to 1:3.

2. Sections, tubes and composite constructions made of sheet steel asset forth in claim 1.

3. Strain hardened sheet steel having a yield point of more than 50 kg./sq. mm., a tensile strength of more than 55 kg./sq. mm., and anelongation of at least 8%, the sheet steel being made of steel having acarbon content of 0.15 to 0.19%, a silicon content of 0.06 to 0.15%, amanganese content of 0.30 to 0.45%, a phosphorus content of less than0.09%, and a sulphur content of less than 0.06% and being provided witha ridge-and-groove profile in which the inner radius of curvature of thegrooves is smaller than three times the sheet thickness and the ratio ofdepth to pitch of the ridge-and-groove profile amounts to 1:15 to 1:3.

4. The sheet steel as set forth in claim 3 in which the phosphoruscontent is-not more than 0.03% and the sulphur content is not more than0.04%.

5. Sheet steel in the form of strain hardened strip having a yield pointof more than 50 kg./ sq. mm., a tensile strength of more than 55 kg./sq. mm., and an elongation of at least 8%, the sheet steel being made ofsteel having a carbon content of 0.15 to 0.19%, a silicon content of0.06 to 0.15%, a manganese content of 0.30 to 0.45%, a phosphoruscontent of less than 0.09%, and a sulphur content of less than 0.06%,having a sheet thickness of 1 to 6 mm. and being provided with aridge-and-groove profile in the longitudinal direction of the stripleaving free narrow marginal zones, the inner radius of curvature of thegrooves being smaller than three times the sheet thickness and the ratioof depth to pit-ch of said ridgeand-groove profile amounting to 1:15 to1:3.

6. Strain hardened sheet steel having a yield point of more than 50 kg./sq. mm., a tensile strength of more than 55 kg./sq. mm, and anelongation of at least 8%, the sheet steel being made of steel having acarbon content of less than 0.30% and being provided with aridge-andgr-oove profile in which the inner radius of curvature of thegrooves is smaller than three times the sheet thickness and the ratio ofdepth to pitch of the ridge-and-groove profile amounts to 1:15 to 1:3,said sheet steel comprising perpendicularly to the direction of thegrooves, alternating bent and stretched zones in relation to the pitchof the grooves, the bent zones corresponding in the proportion of halfthe pitch to the grooves and the stretched zones being interposed.

References Cited by the Examiner UNITED STATES PATENTS 1,868,302 7/1932Auger 29-180 1,982,243 11/1934 Black 29-180 2,089,242 8/ 1937 Whitesell29180 2,160,677 5/1939 Romanofi? 29180 DAVID L. RECK, Primary Examiner.

I-IYLAND BIZOT, R. O. DEAN, Assistant Examiners.

1. STRAIN HARDENED SHEET STEEL HAVING A YIELD POINT OF MORE THAN 50KG./MM., A TENSILE STRENGTH OF MORE THAN 55 KG./SQ. MM., AND ANELONGATION OF AT LEAST 8%, THE SHEET STEEL BEING MADE OF STEEL HAVING ACARBON CONTENT OF LESS THAN 0.30% AND BEING PROVIDED WITH ARIDGE-ANDGROOVE PROFILE IN WHICH THE INNER RADIUS OF CURVATURE OF THEGROOVES IS SMALLER THAN THREE TIMES THE SHEET THICKNESS AND THE RATIO OFDEPTH TO PITCH OF THE RIDGE-AND-GROOVE PROFILE AMOUNTS TO 1:15 TO 1:3.